Process of refining diesel fuel with nitrogen dioxide



United States Patent 3,135,680 PROCESS OF REFINING DIESEL FUEL WITH NITROGEN DIOXIDE William L. Fierce and Roger L. Weichman, both of Crystai Lake, 111., assignors to The Pure Oil Company, Chicago, 11]., a corporation of Ohio No Drawing. Filed Sept. 11, 1961, Ser. No. 137,028 9 Claims. (Cl. 208-45) This invention relates to new and useful improvements in processes for refining mineral oil fractions which contain a substantial quantity of sulfur compounds. This invention is further concerned with a process for refining petroleum fractions of the diesel-fuel boiling range to produce diesel fuels of improved cetane number and odor.

Petroleum fractions, e.g., naphthas, kerosines, gasolines, fuel oils, diesel oils, lubricating oils, waxes, etc., as normally obtained from petroleum, often have unsatisfactory odor characteristicsresulting from the presence of malodorous mercaptans and'other sulfur compounds. The

removal of these malodorous constituents has often proved difficult by ordinary refining procedures. In the past, removal of mercaptans has been accomplished to some extent by clay treating and by treatment with chemicals which form readily extractable derivatives. In some cases, the removal of mercaptans and other sulfur compounds has been impractical and the sour petroleum fractions have been treated by a sweetening process in which the sulfur compounds, such as mercaptans, are converted to derivatives of lesser odor.

In the past, petroleum fractions have been treated with a variety of chemicals to give products with improved odors. Naphthas have been treated with absorbents of various types, and have been treated with various amines during distillation to prevent formation of malodorous constituents. Petroleum fractions have been subjected to solvent extraction with various acidic materials such as sulfur dioxide, phenol, and concentrated organic acids 'to extract color-forming and odor-forming constituents.

It is therefore one object of this invention to provide a new and improved process for treating petroleum fractions of the diesel-oil boiling range to increase cetane number, eliminate mercaptans, and improve the odor characteristics.

A feature of this invention is the provision of a process in which a sour petroleum fraction of the diesel-oil boiling range is treated with gaseous nitrogen dioxide at a relatively low temperature, and then washed with water to remove water-soluble products.

7 Another feature of this invention is the provision of a process in which a sour petroleum fraction is washed with aqueous caustic and treated with gaseous nitrogen dioxide at a relatively low temperature, and then washed with water to produce a petroleum product of improved odor and cetane number, and a copper-strip corrosion test (ASTM D-l30) rating not greater than 1.

Still another feature of this invention is the provision of a process in which a petroleum fraction is treated with gaseous nitrogen dioxide at a relatively low temperature and subjected to a decolorizing treatment, such as vacuum distillation, clay treating, acid treating, etc., to remove colored reaction products, and thus obtain a product of improved odor and reduced sulfur content.

Other objects and features of this invention will becomeapparent fiom time to time throughout the specification and claims as hereinafter related.

In measuring the relative odor of petroleum products 'it has not been possible to develop a precise, quantitative measure of odor which is entirely. independent of the individual who evaluates the odor. Nevertheless, there are certain procedures for rating odors which have been "used in the petroleum industry. Odor evaluation stand- 3,135,580 Patented June 2, 1964 ards and methods have been proposed by a joint committee of the ASTM and TAPPI. A modification of this procedure has been used extensively in the evaluation of the odor of commercial petroleum products. In a typical petroleum company, an odor panel is selected consisting of several, e.g., 10 to 20 or more, individuals who have been tested for their ability to discriminate between and match different odors. One test for' selection of panel members involves correctly matching a series of chemical odors such as very dilute odors of acetic acid, phenol, toluene, and benzene. A second test involves a matching of a variety of different naphthas by odor from a single manufacturing source. A third test involves the matching of mineral spirits obtained from different manufacturers. By use of these screening tests, it is possible to select a panel of 10 to 20 individuals who are especially discriminating in evaluating odors of petroleum products. In the rating of odors of petroleum fractions such as an odorless naphtha, a numerical rating scale has been established to describe odor quality.

When evaluating the odor of petroleum naphthas, the following procedure is used. The members of the odor panel are requested to avoid contact with contaminating odors, e.g., smoking, etc., for at least /2 hour prior to the test. The odor evaluation is carried out in an air-conditioned room, at about F., whichis as freeas possible from extraneous odors. Each member of the test panel rates the odor of a product separately. A non-member of a panel conducts the test and is present to record any pertinent comments made regarding the odor. To eliminate bias, the product samples are coded, and the panel members aretold onlythe .type of product being rated. To avoid .odor fatigue, no more than three samples are rated at any one time. Any additional ratings are spaced by at least three hours. A total of seven panel members rate the product and the average of these opinions is reported as the odor rating.

In preparing the naphtha for odor evaluation, a 35-ml. representative portion is poured into a clean, odor-free, eight-ounce, French square bottle. The bottle is sealed with a clean, odor-free, screw-on cap. The same sample is used by all members of the panel. The type bottle used in the evaluation is the same as used in the screening tests for selection of the panel member. The panel member evaluates the odor of the naphtha by removing the cap from the bottle, placing his nose at the bottle mouth and snifling the odor. He checks the intensity of odor and for any foreign or undesirable odor. that may be present and then numerically rates the odor using the above-described scale. This method is called the wetodor of the naphtha. V

In carrying out this invention, we have found that it is possible to convert sour diesel-fuel fractions to products having very good odor ratings and which are substantially improved in cetane' number. Our process for deodorizing diesel fuels and improving the cetane number thereof consists essentially of two. steps. First, the oil is treated with gaseous nitrogen dioxide at a relatively low temperature, preferably in the range from about 0 to 40 C. The amount of nitrogen dioxide required is dependent upon the degree of cetane number improvement desired. The product which is obtained upon treatment of the dieselfuel with nitrogen dioxide ranges in color from yellow to dark orange. Secondly, the treated oil is washed with water until all water-soluble acidic material is removed. The final product is a clear diesel fuel-oil having a color essentially the same as the product obtained in the first step. The oil can be dried before use if necessary. In some cases, the product obtained by this treatment is excessively corrosive, as measured by the copper-strip corrosion test (ASTM method D-130). In such cases, the product can be converted to one having a satisfactory corrosion rating by washing with aqueous alkali (NaOH, KOH, NH OH, etc.) before and/or after treatment with nitrogen dioxide, but prior to the final wash step.

The mechanism by which this process operates to remove sulfur compounds and to improve the cetane number of diesel fuel-oils is not known with certainty. It is known that nitrogen dioxide will react with a variety of organic compounds and sulfur compounds to form oxidation products which may or may not contain nitrogen. The nitrogen dioxide-tr'eated diesel fuels obtained by our process probably contain reaction products of nitrogen dioxide with various components of the fuel oil since the nitrogen dioxide is taken up quantitatively by the oil and no nitrogen oxide by-products are given off. However, the effect of these reaction products on cetane number and on odor is not disclosed in the prior art. The increase in cetane number is also obtained when this treatment is given to fuel oils having a low sulfur content. The increase in cetane number may be due to the presence of compounds such as nitrates, nitrites, sulfoxides, and sulfones, but the presence of these compounds has not been established and it is not known with certainty just what causes the increased cetane number of the fuel. However, regardless-of the identity of the reaction products and the mechanisms of the reactions involved,

the result of our process is the formation of a diesel fueloil with improved odor and substantially improved cetane number.

We have found that this process is generally applicable to mineral oil fractions boiling in the diesel-fuel boiling range, e.g., 177 to 330 C. The process is not applicable to the treatment of light petroleum distillates inasmuch as the color of the product and the increase in cetane number are objectionable properties in naphthas and gasolines. The treatment with nitrogen dioxide is carried out by bubbling gaseous nitrogen dioxide, either with or without an inert diluent gas, through the diesel fuel-oil at a relatively low temperature, preferably about 40 C. The nitrogen dioxide is added to the sour diesel oil in an amount sufficient to convert the malodorous sulfur compounds to odor-free products and improve the cetane number of the product. The nitrogen dioxide is used in an amount not less than the stoichiome'tric amount required to react with substantially all of the sulfur compounds in the diesel fuel-oil, and larger proportions of nitrogen dioxide may be used if desired. When relatively small amounts of nitrogen dioxide are reacted with a sour diesel fuel-oil, all of the nitrogen content of the treating gas is retained in the oil in some form of chemical combination. The improvement in cetane number of the fuel is generally in proportion to the amount of nitrogen combined with the fueloil in the nitrogen dioxide treatment. Water- Washing of the treated fuel, or water-washing following a prior wash with aqueous caustic is generally effective in producing a non-corrosive product.

The following non-limiting examples are illustrative of the scope of this invention.

Example I In one experiment, 1,000 mlrof untreated diesel fueloil was charged to a' 3,000 ml., 3-necked flask equipped with a stirrer, thermometer, and bubbler tube. The oil .which was used in this experiment was a refinery product rosive as a result of the treatment.

4 known as untreated range oil. The oil had the following distillation range: I.B.P. 178 C., 5% 193 C., 50% 232 C., 273 C., and BF. 288 C. It had a total sulfur content of about 0.53% wt., was rated sour by the doctor test, and had an odor rating of about 7. This oil is normally converted to a No. 1 furnace oil, also usable as a diesel fuel-oil, by doctor treatment. The oil undergoing treatment had an initial cetane number of 48.7. In this experiment, the oil was maintained at about 5 C. by a Dry Ice-acetone bath. Nitrogen dioxide was bubbled in over a period of minutes at a rate such that 3.1 g. were added to the oil. The resulting product was a slightly cloudy, medium-orange liquid. This treated fuel oil was then washed five times with 400-ml. portions of distilled water. The product was then dried by filtering through a double thickness of Reeve Angel paper (filter paper used for removing entrained water). The product was a fairly dark orange liquid which was doctor sweet and had an odor rating of about 4. The cetane number of the fuel had increased from an initial value of 48.7 to a treated value of 5 1.8. Thus, the addition of 3.1 g. to 1000 ml. diesel fuel oil resulted in an increase of 3.1 in cetane number. The treated .oil was reduced by about 25% in total sulfur content. The diesel oil which was obtained in this process was doctor sweet, substantially improved in odor, and appreciably improved in cetane number.

. Example [I In another experiment, 1000 ml. untreated range oil, as described in Example I, was charged to a 3000-ml., 3- necked flask equipped with a stirrer, thermometer, and bubbler tube. The oil was maintained at about 5 C. by a Dry Ice-acetone bath. Over a period of four hours, nitrogen dioxide in the amount of 6.2 g. was introduced through the bubbler tube for reaction with sulfur compounds in the diesel oil. At the end of this period, the diesel oil had changed to a fairly dark amber-orange product which was slightly cloudy. The treated oil was then washed seven times with 100-ml. portions of distilled water. The oil was then filtered through a double thickness of Reeve Angel paper to remove water. The treated'and dried product was a clear, fairly dark orange liquid with substantially improved odor. The treated fuel oil was doctorsweet, and had an odor rating of about 5 as compared to an odor rating of 7 for the untreated range oil. The treated oil had a cetane number of 53.9 which was an increase of 5.2 units over the untreated oil. 7

Example Ill In another experiment, 1,000 ml. diesel fuel-oil was charged to a 3,000 ml., 3-necked flask, as in Example I. The oil which was used had the same boiling range as that used in Example I, an odor rating of 8, a total sulfur content of 0.53% wt., and an initial cetane number of 48.7. This oil was non-corrosive and had a copper-strip corrosion test rating of 1a (compared to copper-strip test standard) as measured by ASTM D- copperstrip corrosion test, i.e., 3-hour immersion of copper strip at 122 F. In this experiment, the oil was treated with nitrogen dioxide at about 5 C. until nitrogen dioxide was taken up by the oil in a concentration of about 2.17 lb./bbl. (42 gal./bbl.). In this experiment, the total sulfur content was reduced by about 25 and the odor rating was reduced to 5. The oil was washed 6 times with 400-ml. portions of water to remove acidic, water-soluble, reaction products. The oil which was obtained had a cetane number of 53.9, but had become excessively cor- When this oil was measured by immersion of a copper strip for 3 hours at 122 F. in accordance with the ASTM copper-strip corrosion test (method D-130), it was found to have a corrosion rating of 20 (compared with copper-strip corrosion test standard).

A like portion of the same sour oil was treated with nitrogen dioxide to a concentration of 3.15 lb./bbl., at

,5 C., as in the above-described experiment. In this experment, however, the nitrogen-dioxide-treated oil (a ZOO-ml. portion) was washed 6 times with 50-ml. portions of 0.4 N NaOH, followed by 3 washes with 50-ml. portions of water. Following this washing procedure, the oil was filtered through a double thickness of No. 230 Reeve Angel filter paper to remove entrained water. The oil which was treated in this manner was reduced about 25% in total sulfur content and had an odor rating of 4. This oil was tested for corrosivity using the ASTM copper-strip corrision test and had a corrosion rating of 1b (when compared with the copper-strip corrosion standard).

In other experimental work we have found that if the sour oil is washed with aqueous caustic prior to nitrogen dioxide treatment, and given a simple Water washing following nitrogen dioxide treatment, the resulting product has an acceptable corrosion rating (not in excess of 1, as measured by the ASTM copper-strip corrosion test, 3-hour immersion at 122 F.). If desired, the wash with aqueous caustic may be given to the oil both before and after treatment with nitrogen dioxide and followed with a water wash to remove water-soluble acidic products. When the oil is treated in this manner, there is a slight loss in cetane number improvement although the cetane number of the finished product is substantially higher than the untreated oil. The wash with aqueous caustic can be carried out using other alkalies such as potassium hydroxide, lithium hydroxide, ammonium hydroxide, etc.

Example IV While this process is primarily concerned with desulfurizing sour diesel fuel-oils, and improving the odor characteristics thereof, it is also applicable to improving the cetane number of diesel fuel-oils which have been previously desulfun'zed to a very low sulfur content. When an oil of the diesel-fuel boiling range which has previously been desulfurized to a low sulfur content is treated with nitrogen dioxide there is a substantial improvement in the cetane number of the fuel. The fuel oil can be treated with nitrogen dioxide in amounts varying from a very small fraction of 1% up to as much as 10% of the weight of the fuel oil. When this-treatment is used, the oil is washed with water (and aqueous alkali if necessary) to remove water-soluble acidic material and produce a fuel having satisfactory corrosion characteristics.

In one experiment, a hydrogenated furnace oil having very low sulfur content was treated with nitrogen dioxide. This oil had a boiling range substantially the same as the oil used in the other experiments, but had a total sulfur content of about 0.05% wt. The oil had an initial odor rating of 4, ASTM color rating of 1, copper-strip corrosion test rating of 1a, and cetane number of 45.0. This oil was treated at 2 C. with nitrogen dioxide until it had taken up nitrogen dioxide to a concentration of 1.60 lb./bbl. The nitrogen-dioxide-treated oil (about 990 ml.) was washed ten times with 400-ml. portions of distilled water. The product oil had an odor rating of 4, copperstrip corrosion test rating of 1a, and ASTM color rating of +4. The cetane number of the fuel had increased to 50.0.

In another experiment, a 990-ml. portion of the nitrogen dioxide-treated oil prepared as just described was washed five times with 400-ml. portions of 0.4 N NaOH, followed by three washes with 400-ml. portions of distilled water. There was no significant difference in corrosion, odor, or cetane number of the finished oil, but it was slightly lighter in color.

In still another experiment, the nitrogen dioxide treatment was carried out at 38 C. to a nitrogen dioxide concentration of 1.57 lb./bbl. Part of the nitrogen dioxidetreated oil was washed ten times with 400-ml. portions of distilled water, and part of the oil was Washed five times with 400-ml. portions of 0.4 N NaOl-I followed by three washes with 400-ml. portions of distilled water. In each case, the finished oil had a cetane number of 51.5, corrosion rating of 1a, odor rating of 5, and color rating of 3 /24.

Example V In some cases it is desirable to convert the nitrogen dioxide-treated oils into products which are completely free of the colored materials formed during nitrogen dioxide treatment. The exact nature of the colored reaction products is not known and the separation of these colored products from the treated oil requires fairly drastic treatment. The colored reaction products can be removed by severe sulfuric acid treatment, by vacuum distillation of the oil away from the higher boiling, colored products, or by adsorption (e.g., clay-treating or treating with silica gel). In most cases, however, the separation of the oil from the colored reaction products produces a product which is sweet, but which has no higher cetane number than the oil prior to nitrogen dioxide treatment. This oil is usable as a furnace oil, but has no particular advantage as a diesel fuel.

A light cycle oil having a boiling range of 228330 C. and a total sulfur content of about 1% (mercaptan content of 0.009%) was treated with nitrogen dioxide in an amount of 1.32 lb./bbl. at 38 C. After treatment with nitrogen dioxide the total sulfur content was substantially unchanged (the nitrogen dioxide treatment tends to reduce the content of mercaptan and sulfide compounds, but does not affect complex, high-molecular- Weight sulfur compounds in the oil), but the mercaptan content was reduced by more than As a result of this treatment, the color of the oil increased from 1+ to +4 /2 dil. The treated oil (1200 ml.) was filtered, washed three t mes with 300-ml. portions of water, and then filtered to remove entrained water. A 1000-ml. portion of the product was distilled in glass apparatus at 15 mm. Hg. During the distillation, successive -ml. cuts of the distillate were taken and measured for color properties. The first 20% of the distillate had a. color rating of 1+. The next 50% of the distillate had a color rating of +1 /2. The remainder of the distillate (distillation was stopped at 883 ml.) had a color rating of +2. The residue from the distillation was not measured for color, but contained substantially all of the darkcolored reaction products produced during the nitrogen dioxide treatment. The oil which is produced by nitrogen dioxide treatment followed by vacuum distillation is usable as a furnace oil, or as a diesel fuel (although it has no increase in cetane number), and it is substantially reduced in mercaptan sulfur content.

Example VI In another experiment, when the diesel fuel-oil was treated with nitrogen dioxide, washed, and distilled at atmospheric pressure, an incomplete separation from the colored reaction products was obtained. In that experiment, a substantial portion of the colored reaction products distilled over with the oil so that the distillate was highly colored, although slightly less intense than the treated oil. Additionally, the distillate from the highertemperature, atmospheric-pressure distillation was found to contain mercaptan sulfur, apparently resulting from decomposition of residual sulfur compounds during distillation. From these experiments, it appears that the separation of the nitrogen dioxide-treated oil from the colored reaction products by distillation is feasible only if carried out at reduced pressure. A satisfactory separation of the oil from the colored reaction products can be accomplished by distillation at any suitable pressure less than about 100 mm. Hg.

Example VII A No. 2 fuel oil having a total sulfur content of about 0.83% (mercaptan content of 0.012%) was treated with nitrogen dioxide at 2 C. to a concentration of 1.07 lb./ bbl. The nitrogen dioxide-treated oil (658 ml.) was 7 washed three times with BOO-ml. portions of water. The oil which was produced had a dark color (ASTM rating +7). This oil was contacted with Filtrol 60 clay, batchwise (at a concentration of 20 lb./bbl.) at room temperature for 40 minutes. The color was reduced from +7 to 3. The cetane number of the oil prior to nitrogen dioxide treatment was 41.2. After nitrogen dioxide treatment, the oil had a cetane number of 43.7 which decreased to 42.7 after clay treatment. Other clays of the type used for decolorizing oils can be used in the treatmentof a nitrogen dioxide-treated oil. Attapulgus clay has been found particularly effective in decolorizing nitrogen dioxide-treated oils.

Example VIII 7 In another experiment, a No. 2 fuel oil having a total sulfur content of 0.36% wt. was treated with nitrogen dioxide at 2 C. to a concentration of 1.37 lbs./bbl. The nitrogen dioxide-treated oil was washed 6 times .with 400-rnl. portions of water. As a result of this treatment the cetane number of the oil increased fiom 40.5 to 45.0. The color of the oil increased from ASTM rating of less than 1 to +4.- The treated oil (990 ml.) was then percolated through a column of silica gel 11% inches tall (concentration 51.5 lbs./bbl.) to remove the colored reaction products. This treatment reduced the color from +4 to 1+. The treatment also reduced the cetane number from 45.0 to 41.8. As a result of this treatment, it appears .that the colored reaction products can be effectively removed from the nitrogen dioxide-treated oil without complete loss of the cetane-number improvement resulting from the nitrogen dioxide treatment.

From these and other experiments which We have carried out, we have found that the treatment of sour diesel fuel-oils with nitrogen dioxide in an amount at least equal to the stoichiometric amount required for reaction with sulfur compounds in the oil reduces the odor rating of the oil substantially, and renders the oil doctor-sweet.

We have found that there is an increase in cetane number of the oil which is generally proportional to the amount of nitrogen dioxide reacted with the oil. When desulfurized oils are treated with nitrogen dioxide, there is obtained a substantial increase in cetane number together with the formation of dark-colored reaction products. While the above examples used nitrogen dioxide in the amount of about 03-06% wt. of the oil, greater quantities of nitrogen dioxide may be used,'up to about wt., with substantial increases in' the cetane number of the fuel oil. At relatively high proportions of nitrogen dioxide reacted with the oil, the increase in cetane numher is not as great in proportion to the nitrogen dioxide added, but the improvement does increase with greater concentrations of nitrogen dioxide. The nitrogen dioxidetreated oil must be washed with water to remove waterafter the nitrogen dioxide treatment but prior to the final Water-wash step. Where a product of better color is required, the treated oil can be separated from the colored reaction products by acid treatment, vacuum distillation, or adsorption.

While we have described this invention fully and completely with special emphasis upon certain preferred embodiments, we wish it to be understood that within the scope of the appended claims this invention may be practiced otherwise than as specifically described.

The embodiments of the invention in which an exclusive property or privilege is claimed are as follows:

1. A method of producing a diesel fuel of improved cetane number which consists in contacting a petroleum fraction of the diesel-fuel boiling range, which has been subjected to previous chemical treatment, with nitrogen dioxide as the sole oxidant at about 040 C., and washing the treated product with suflicient washing agent from the group consisting of water and aqueous alkali solution to remove substantially all Water-soluble products, the final washing being with water.

2. A method in accordance with claim 1 in which the petroleum fraction is washed with aqueous alkali prior to treatment with nitrogen dioxide.

3. A method in accordance with claim 1 in which the petroleum fraction is washed with aqueous alkali after treatment with nitrogen dioxide.

4. A method in accordance with claim 1 in which the nitrogen dioxide is used in an amount not less than the stoichiometric amount required to react with all of the sulfur compounds in the products.

5. A method in accordance with claim 1 in which sufficient nitrogen dioxide is used to effect a substantial increase in cetane number of the fuel.

6. A method in accordance with claim 1 in which the diesel fuel is a petroleum fraction having a boiling range from about 177 to 330 C. and a sulfur content of about 0.05 to 1.0% wt.

7. A method in accordance with claim 6 in which the fuel is dried after Washing with water.

8. A fuel oil produced in accordance with claim 1.

9. A method of producing a diesel fuel of improved cetane number which consists in contacting a petroleum fraction of the diesel-fuel boiling range with nitrogen dioxide, as the sole oxidant, at about 0-40 C.; washing the treated product with sufficient washing agent from the group consisting of water and aqueous alkali solution to remove substantially all water soluble products, the final Washing being with water.

' References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Ephraim: Inorganic Chemistry, 5th edition, lnterscience Publishers 1116., N.Y.C., NY. (1949), pages 715. and 716.

tint 

1. A METHOD OF PRODUCING A DIESEL FUEL OF IMPROVED CETANE NUMBER WHICH CONSISTS IN CONTACTING A PETROLEUM FRACTION OF THE DIESEL-FUEL BOILING RANGE, WHICH HAS BEEN SUBJECTED TO PREVIOUS CHEMICAL TREATMENT, WITH NITROGEN DIOXIDE AS THE SOLE OXIDANT AT ABOUT 0*-40*C., AND WASHING THE TREATED PRODUCT WITH SUFFICIENT WASHING AGENT FROM THE GROUP CONSISTING OF WATER AND AQUEOUS ALKALI SOLUTION TO REMOVE SUBSTANTIALLY ALL WATER-SOLUBLE PRODUCTS, THE FINAL WASHING BEING WITH WATER.
 8. A FUEL OIL PRODUCED IN ACCORDANCE WITH CLAIM
 1. 